<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <script>
        var num = prompt('请输入班级学生人数');
        var sum = 0,
            aver = 0;
        for (var i = 1; i <= num; i++) {
            var score = prompt('请输入第' + i + '个学生的成绩');
            sum += parseFloat(score);
            console.log(sum);
        }
        aver = sum / num;
        alert('班级学生总成绩为' + sum);
        alert('班级学生平均分为' + aver);
    </script>
</head>

<body>

</body>

</html>